The present novel concept broadly relates to fluid suspension systems and, more particularly, to a gas spring assembly having an improved piston construction adapted for use in offset mounting conditions.
It is to be specifically understood that the subject novel concept is capable of broad use in a wide variety of suitable applications and environments and can be used in association with gas spring assemblies of any suitable size, type and/or configuration without departing from the principles thereof.
One category of known gas spring assemblies, referred to in the art as rolling lobe-type gas springs, typically includes a top plate, a piston and a flexible sleeve secured therebetween. The flexible sleeve forms a lobe that rolls up and down an outer side wall of the piston in response to loads applied to the top plate and/or piston. In such assemblies, the piston is normally formed from either a metal material, typically steel, or a plastic material. Each construction has numerous benefits as well as some disadvantages, and the selection of one construction versus the other will vary from application-to-application.
FIG. 1 illustrates one example of a prior art gas spring 10 of a generally known construction secured along a structural member STM, such as a component of a vehicle, for example. Gas spring 10 includes a top or bead plate 12 and a piston 14 disposed in spaced relation thereto. A flexible sleeve 16 is secured between the bead plate and piston and generally defines a spring chamber 18 formed therebetween.
Flexible sleeve 16 includes an upper mounting bead 20 that is captured by bead plate 12 in a typical manner, such as by crimping the peripheral edge of the bead plate around the upper mounting bead. Upper mounting studs 22 are supported on bead plate 12 and project outwardly therefrom. A gas passage 24 extends through one of the upper mounting studs and is in fluid communication with spring chamber 18.
Flexible sleeve 16 also includes a lower mounting bead 26 that is secured on piston 14 using an end closure 28. A threaded bumper mount 30 receives a lower mounting stud 32 that extends through end closure 28, piston 14 and structural member STM. Threaded bumper mount 30 and end closure 28 are secured on the piston by a first washer 34 and threaded nut 36. Additionally, the gas spring assembly is secured to structural member STM using a second washer 38 and a second threaded nut 40. As lower mounting stud 32 is tensioned by the first threaded nut, bumper mount 30 secures end closure 28 on piston 14 thereby capturing and retaining lower mounting bead 26 of flexible sleeve 16. A jounce bumper 42 is shown as being secured on bumper mount 30 along end closure 28.
Piston 14 is exemplary of known steel piston constructions and includes an outer shell 44 along which flexible sleeve 16 is secured and rolls. A base plate 46 is received within a lower, open end of outer shell 44 and is typically secured therein by welding the base plate and outer shell together, as indicated by all-around weld WD1. A central mounting hole 48 extends through base plate 46 and lower mounting stud 32 extends therethrough. Outer mounting holes 50 are spaced radially outwardly from the central mounting hole and are suitable for receiving fasteners (not shown). Weld nuts 52 are secured, such as by welded joints WD2, on base plate 46 adjacent outer mounting holes 50. Additionally, structural member holes 54 are in alignment with the outer mounting holes and weld nuts for receiving a suitable fastener (not shown). A center column 56 extends between outer shell 44 and base plate 46 and is typically secured on the base plate by a welded joint WD3.
Another embodiment of a generally known construction is shown in FIG. 2 and has like items that will be shown and/or described using like reference characters. Additionally, new or modified features and/or components are shown and described using new reference characters. A primary difference between gas spring 10 shown in FIG. 1 and piston 58 of gas spring 60 shown in FIG. 2 is that piston 58 is molded from a plastic material. As such, piston 58 is typically a unitary construction formed from a single material. Piston 58 includes an outer shell portion 62 and an inner support portion 64. Outer shell portion 62 is interconnected with inner support portion 64 through a plurality of radial wall portions 66. Inner support portion 64 extends between an upper end wall 68 and a lower end wall 70. The upper end wall engages end closure 28 and the lower end wall is supported on a structural member STM.
As piston 58 is of a molded construction, it will be appreciated that typical molding conventions and techniques apply to the manufacture thereof and are used in forming piston 58. For example, it is desirable to maintain a substantially uniform wall thickness when an injection molding process is utilized. As such, piston 58 includes numerous cored areas 72 of a variety of shapes, sizes and configurations. Thus, certain limitations in the shape and/or configuration of piston 58 and the walls thereof may exist.
One benefit of producing a piston from plastic is that the piston can often be injection molded as a complete or nearly complete component as disclosed in commonly owned, co-pending U.S. application Ser. No. 11/398,835, filed 6 Apr. 2006, the entire disclosure of which is expressly incorporated herein by reference. As a result, costs associated with physically assembling the piston can be significantly reduced or eliminated. Additionally, it is well understood that gas springs are commonly exposed to harsh environments, such as in vehicle suspension applications in which water, dirt, salt and other materials are present. Another benefit is that pistons formed from a plastic material are often less susceptible to exposure of this kind.
A need exists in the industry to provide a piston for use in offset mounting arrangements. For example, it is sometimes desirable to position a gas spring on a vehicle in such as manner that the piston thereof is secured to a support arm in an offset mounting arrangement, such as to prevent the components of the gas spring from inadvertently contacting the tire. Known piston assemblies that are suitable for use in such offset mounting arrangements are generally heavy duty in order to handle the additional stresses imposed by the offset mounting condition. Consequently, a need exists for an offset mounting design that can still be manufactured as a lightweight composite material. Present composite piston designs are not adapted for offset use and, for example, often include a central support structure for securing the gas spring piston to a central mounting surface. Still other composite piston designs are used in conjunction with a metal mounting plate to allow for offset mounting.
Moreover, an offset mounting arrangement for a composite piston used with a gas spring assembly should preferably include the advantages of reduced weight, reduced number of components, simplified manufacturing process and cost improvements when compared to other offset piston designs.
Accordingly, an improved piston and gas spring assembly including the same have been developed that overcome these and other disadvantages.